strcspn(3) does not work this way, fix SIGSEGV on unknown comments

$OpenBSD: patch-ogg123_vorbis_comments_c,v 1.1 2009/07/17 08:20:37 weerd Exp $
--- ogg123/vorbis_comments.c.orig	Wed Jul  8 18:44:47 2009
+++ ogg123/vorbis_comments.c	Wed Jul  8 18:45:13 2009
@@ -72,7 +72,7 @@ char *lookup_comment_prettyprint (char *comment, int *
 
   /* Use default formatting */
   j = strcspn(comment, "=");
-  if (j) {
+  if (j != strlen(comment)) {
     *offset = j + 1;
     s = malloc(j + 2);
     if (s == NULL) {
